The present invention relates to a data storage device including a recording medium on which servo information for positioning a read/write head is written, and more specifically to a data storage device having characteristic servo information written thereto.
A hard disk drive has a magnetic head for reading user data stored on a magnetic disk and for writing user data on the magnetic disk. The magnetic head is attached to a rotary-type actuator mechanism which is swung by a voice coil motor (VCM).
When the magnetic head writes or reads user data, the actuator mechanism is driven, and thus the magnetic head is moved to a predetermined track and positioned. Movement of the magnetic head to a predetermined position is controlled by using servo information stored on the magnetic disk as a clue.
On a magnetic disk contained in a hard disk drive or the like, a plurality of data tracks are concentrically formed and, moreover, identification information and burst patterns are stored along radial directions of the disk in advance. The identification information and the burst patterns constitute servo information. The identification information is information indicating track addresses of respective data tracks. Based on the identification information read by a magnetic head, determination can be made as to an approximate position of the magnetic head, that is, as to which data track a position of the magnetic head corresponds to. The burst patterns are constituted by a plurality of burst pattern rows in which areas having signals stored therein are arranged along the radial directions of the disk at constant intervals and of which signal storage areas have mutually different phases. It is possible to detect a precise position of the magnetic head, that is, a deviation indicating how far the position of the magnetic head deviates from the data track to which the magnetic head corresponds, based on a signal (position error signal: PES) outputted from the magnetic head in accordance with the burst pattern.
A read or write of user data with respect to the magnetic disk is performed in a state where the magnetic disk is rotating after the following operations: the magnetic head is moved while an approximate position of the magnetic disk is being determined based on the identification information read by the magnetic head, whereby the magnetic head is made to correspond to a specific data track; and then the magnetic head is precisely positioned at the specific data track based on a signal outputted from the magnetic head in accordance with the burst patterns. Such a series of operations are referred to as a seek operation. Even in a period when user data is being read or written, feedback control is performed so that the magnetic head is positioned at a fixed position relative to the specific data track based on the signal outputted from the magnetic head in accordance with the burst patterns. Such an operation is referred to as a track following operation.
Servo information is written on a magnetic disk as a recording medium in a manufacturing process before a hard disk drive is shipped as a product. It is required that the servo information be written precisely in order to write or read user data accurately.
In a hard disk drive, as a recording density increases, a magnetoresistance (MR) head or giant magnetoresistance (GMR) head using the magnetoresistance effect is used as a reproducing head (read head), and an inductive head is used as a recording head (write head). The two heads are attached to a same magnetic head slider and constitute a hybrid magnetic head.
As described above, one existing hard disk drive uses a rotary-type actuator as an actuator for driving a magnetic head. Therefore, when the magnetic head accesses a predetermined position on a magnetic disk, a trajectory of the magnetic head forms a circular arc. Accordingly, over the range of the most inner track to the most outer track of the magnetic disk, the center line of a magnetic head slider and a tangent line of a data track on the magnetic disk are not parallel but intersect with a different angle depending on each data track. The intersecting angle is referred to as a skew angle.
The existence of the skew angle inevitably generates a read write offset described later. Specifically, when a read head is positioned at a proper position on a servo track of the magnetic disk (such a state is referred to as “on track”), a write head cannot be positioned at a proper position on the servo track (such a state is referred to as “off track”). The position difference between the centers of the read and write heads is a read write offset.
In a hard disk drive, when user data is written on a magnetic disk (recording), a magnetic head slider is moved to a target position by reading servo information recorded on a servo track by use of a read head, the read head is made to be “on track” on a servo track, and then the user data is written on a data track of the magnetic disk by a write head. On the other hand, when the user data written on the data track is reproduced, even if the read head is made to be “on track” on the servo track, the read head cannot be “on track” on the data track to which the write head has written the user data, due to a read write offset. Accordingly, the user data may not be accurately reproduced sometimes.
Various proposals have been made for solving the above-described problem based on a read write offset. Japanese Unexamined Patent Publication No. 2000-322848, for example, discloses a method in which a measured read write offset value is stored, and an access position is corrected based on the stored read write offset value when user data is reproduced, thus performing positioning control of a magnetic head slider.
The above-described proposal is an effective method for a read write offset but has the following problems.
FIG. 13 is a view showing a relationship between burst patterns BP and a PES. Ideally, it is preferred that the PES is shown by continuous linear lines. However, in reality, the linearity is lost in regions indicated by circles and surrounding regions thereof. Therefore, an error appears in a physical position obtained by conversion based on the PES. Moreover, the loss of the linearity adversely influences a servo control system. In a hard disk drive used heretofore, servo tracks are recorded at a constant track pitch on a magnetic disk. Accordingly, any one of read and write heads is located at a position where linearity of a PES is lost.